An analysis of the development of a number of English and French constructions involving various kinds of subject-verb inversion. The analysis is framed in terms of the principles-and-parameters approach to syntactic theory, and provides strong support for the adoption of this approach in the description and explanation of language change. The book is divided into three parts. The first part presents an overall framework for the analysis of inversion constructions and motivates, on the basis of synchronic data, several parameters which distinguish among the various Romance and Germanic languages. The second part shows how several near-simultaneous syntactic changes in the history of French can be explained as a change in one of the parameters introduced in Chapter One. A notable aspect of this analysis is the way in which the distribution of null subjects is shown to relate to verb-placement. The third part of the book treats verb-movement in the history of English, arguing in detail that the attested changes in this area are due to a change in the internal structure of "infl", a proposal which has important ramifications for the theory of functional heads. Throughout the book, emphasis is placed on the theoretical questions raised by language change. In this connection, the two notions of diachronic reanalysis and parametric change are distinguished.